Liquid-like behavior in solids
The van der Waals approach to predict liquid-vapor coexistence, becomes exact in the limit of weak, long-ranged attractive forces. However, for shorter ranged attractions, the liquid range shrinks and eventually disappears altogether. When the width of the attractive well becomes very small (less than 7% of the diameter of particles), an iso-structural solid-solid transition, reminiscent of the liquid-vapor transition, appears in the crystalline phase. This transition, that should be experimentally observable in certain colloidal suspensions, ends in a critical point. In quasi-two dimensional systems (e.g. confined colloids), this critical point induces the formation of a stable hexatic phase.
Frenkel, D, Bladon, P.B, Bolhuis, P.G, & Hagen, M.H.J. (1996). Liquid-like behavior in solids. Mol. Simul., 16, 127–137.